The invention relates to a system for minimizing vibrational movements of a mass. More specifically, the invention relates to a circuit arrangement for controlling the operation of linearly and actively displaceable means which are conventionally arranged between the body of a vehicle or craft and its wheels, its floats, or the like. Such linearly and actively displaceable means will be referred to in the following text as "displaceable means". Conventional displaceable means shock absorbing devices of this type normally combine spring means with pneumatic or hydraulic displaceable members. The spring elements may comprise steel springs, so-called rubber springs, and/or air springs. It is also known to use hydraulic dampers or friction dampers for achieving an effective damping of impacts and/or vibrations. For example, in connection with the landing gear of aircrafts it is customary to use substantially exclusively shock absorbers comprising a so-called air spring and a hydraulic damper forming in combination a so-called oil air shock absorber. Single chamber shock absorbers are most frequently used and comprise substantially an air spring arranged in parallel to an oil damper or dash pot and this structure is satisfactory for many applications. A disadvantage of this type of structure is seen in its static spring characteristic curve which is by no means optimal. The damping factor is advantageous only for one descent speed. Further, the reaction to excessive speeds to be absorbed results in high load peaks which occur, for example, when the wheel passes over a bump in the ground.
In those instances where the above mentioned single chamber shock absorber is insufficient, it is known to use more complicated structures having characteristics adapted to the particular type of use. Thus, German Patent Publication (DE-OS) No. 2,150,406 discloses an oil pneumatic shock absorber device comprising two air chambers and several oil chambers which are interconnected through valves and/or throttling devices. The improved dynamic characteristic of such a system which has been achieved by such mechanical efforts and expenditures, approximates the optimal dynamic characteristic more closely than is possible with simpler structures. However, in no instance is it possible to realize the optimal dynamic response characteristic by purely mechanical means.
The dynamic response characteristic that must be satisfied by a system for minimizing vibrational movements is determined particularly by the mass of the vehicle or craft and is thus dependent on the size of the payload. Accordingly, the most advantageous dynamic response characteristic may be obtained only when the gross weight including the payload and the weight of the empty craft or vehicle, corresponds to the weight that has been taken into account when designing the system for minimizing vibrational movements. Thus, prior art systemsof this type have, among others, the following disadvantages. The mechanical effort and expenditure is substantial. The total stroke capacity of the system is normally utilized only partially. The response characteristic depends largely on the vehicle mass and thus on the weight of the load.